The present invention relates generally to modem systems. More particularly, the present invention relates to the initialization of a half-duplex facsimile modem system.
The prior art is replete with different types of full-duplex, half-duplex, data, and facsimile modem systems. Many conventional modem systems that communicate over the public switched telephone network (xe2x80x9cPSTNxe2x80x9d) may have an undesirably long connect or initialization time between dial-up and the full rate data mode. In the context of a typical half-duplex facsimile modem connection, the startup time can be up to 12 seconds, which can be rather annoying and inefficient, especially in light of some alternative data communication protocols that take advantage of higher transmission speeds.
The initialization of V.34 (and V.90) modem systems begins with the well known startup procedure set forth in ITU-T Recommendation V.8 (International Telecommunication Union, February 1998). In the context of a V.34 system, the V.8 procedure is performed during Phase 1 of the V.34 initialization routine. The modem devices perform the V.8 procedure to exchange their functional capabilities, e.g., the different operating protocols that are respectively supported by each modem device. In a practical operating environment, up to 3.5 seconds of the overall startup time may be devoted to the completion of the V.8 procedure.
Conventional half-duplex facsimile modem systems may perform the V.8 routine in the same manner as a full-duplex system. However, in a half-duplex facsimile modem system, portions of the full-duplex V.8 procedure may be redundant or unnecessary. Consequently, the length of the V.8 phase associated with the startup of a half-duplex facsimile connection may be much longer than actually required.
A V.34 modem system performs Phase 3 of the initialization routine to adaptively train certain functional components, e.g., the equalizer structure, of the receiving device. The equalizer structure is trained in response to a training sequence that has a fixed length or duration designed for the particular implementation. In conventional systems, the predetermined training sequence length is based on experimental test results. The training sequence length is typically dictated by the answering device, which may communicate the length back to the calling device during the initialization period. In a typical system, the transmission and processing of the training sequence may take up to 4.0 seconds. Although the use of a long training sequence increases the likelihood that the equalizer structure will be effectively trained, the overall startup time also increases in a proportional manner. Consequently, prior art systems do not utilize a training sequence having variable characteristics that result in an optimized convergence or a quick, robust, and efficient convergence.
In view of the increasing demand for quick modem startup times, an improved half-duplex facsimile modem initialization routine having a reduced startup latency would be desirable. However, a modified initialization protocol should include an escape route such that the modem system can remain compatible with traditional startup protocols if the modified protocol is not supported by both modem devices.
The present invention provides techniques to shorten the startup time associated with a data communication system that employs a half-duplex modem device. The quick startup technique communicates capabilities exchange information concurrently with the transmission of an analog answer tone associated with the establishment of a call. This feature obviates the need to perform a conventional V.8 procedure and effectively reduces the startup time for the given communication session. The quick startup technique may also employ a training sequence having a variable length (or time duration) that is selected based upon the present characteristics of the communication channel. The duration of the training sequence may be suitably selected to strike a balance between the startup time and the effectiveness of the training procedure. In a preferred embodiment, the techniques of the present invention may be implemented in a manner that is compatible with conventional initialization routines. Accordingly, if the two modem devices support the procedures described herein, then the system may be initialized in a quick manner. On the other hand, if the two modem devices are not fully compatible with the techniques of the present invention, then the system is capable of escaping to a conventional startup routine.
The above and other aspects of the present invention may be carried out in one form by a method for reducing startup latency associated with a data transmission system having a calling device configured to communicate with an answer device over a communication channel. One illustrative method involves the establishment of a call between the calling device and the answer device, the transmission of an answer signal from the answer device to the calling device, and the sending of a capabilities exchange signal from the answer device to the calling device, where the answer signal and the capabilities exchange signal are transmitted in a concurrent manner.